1. Technical Field
The present invention relates to liquid ejecting heads such as ink jet recording heads and liquid ejecting apparatuses, and particularly relates to liquid ejecting heads that eject liquid through a nozzle by displacing a diaphragm portion defining part of a pressure chamber using a piezoelectric element, and liquid ejecting apparatuses.
2. Related Art
Liquid ejecting apparatuses are apparatuses that include a liquid ejecting head capable of ejecting liquid as a liquid droplet and eject various kinds of liquids from the liquid ejecting head. As a representative example of liquid ejecting apparatuses, an image recording apparatus such as an ink jet recording apparatus (printer) that includes an ink jet recording head (hereinafter, referred to as a “recording head”), for example, and performs recording (printing) by ejecting liquid ink as an ink droplet from the recording head, can be cited. In recent years, liquid ejecting apparatuses have been applied to, in addition to the above-mentioned image recording apparatus, various kinds of manufacturing apparatuses such as display manufacturing apparatuses and the like.
Some existing ink jet recording heads (hereinafter, simply called “recording heads”) have a configuration in which a vibrator unit that includes a plurality of piezoelectric vibrators bonded to a fixing plate, a resin case in which an accommodation space capable of accommodating the vibrator unit is formed, and a flow path unit that is bonded to a leading end portion of the resin case (for example, see JP-A-2001-347660 or JP-A-6-320725) are provided. A vibration plate that defines part of a pressure chamber within the flow path unit is displaced by the piezoelectric vibrator so as to change a volume of the pressure chamber, thereby causing a pressure change in the pressure chamber so that the ink is discharged through a nozzle.
The above-mentioned piezoelectric vibrator is formed by laminating a plurality of members. Each member has electrodes formed on a piezoelectric layer. The electrodes formed between the piezoelectric layers function as internal electrodes (individual internal electrodes, common internal electrodes). External electrodes (individual external electrodes, common external electrodes) connected with the internal electrodes are formed on the outer surfaces of the piezoelectric vibrator by sputtering or the like. When driving signals from a printer main body are applied to the external electrodes via a wiring member, electric fields are supplied to the piezoelectric layers (active portions) sandwiched between the two internal electrodes or between the external and internal electrodes so that the piezoelectric layers are deformed. As a result, the piezoelectric vibrator expands or contracts.
The vibration plate has a diaphragm portion configured of a flexible film for sealing an opening surface of the pressure chamber and an island provided on the flexible film. The island is a portion to which a leading end portion of the piezoelectric vibrator is bonded, and is generally made of a metallic block substantially formed in a rectangular parallelepiped shape. The flexible film circumferentially surrounding the island functions as an elastic film portion. When the piezoelectric vibrator is displaced to contract or expand, the island is displaced, whereby a volume of the pressure chamber is changed. The change in the volume of the pressure chamber causes a change in the pressure applied to the ink within the pressure chamber and, making use of this pressure change, the recording head ejects the ink through the nozzle. In JP-A-2001-347660, a problem is described that a fixing plate which is bonded to a base end portion on one side surface in a laminating direction of the piezoelectric layers and electrodes limits the displacement of the piezoelectric vibrator. More specifically, a portion of the piezoelectric vibrator that is on the opposite side to the fixing plate in the laminating direction has a larger displacement than the portion on the fixing plate side (especially, changes largely at a time of contraction). Accordingly, in JP-A-2001-347660, in order to suppress the above problem from occurring, a configuration in which an amount of displacement is suppressed at a portion on the opposite side to the fixing plate is disclosed. Further, in JP-A-6-320725, a configuration is disclosed with which fatigue fracture of an elastic film (thin portion) and cavitation, caused by driving of a piezoelectric vibrator bonded to an island of a vibration plate, are suppressed.
These piezoelectric vibrators respectively have external electrodes formed on both side surfaces thereof in the laminating direction of the piezoelectric layers and electrodes. In these respective piezoelectric vibrators, the thickness of the piezoelectric layers positioned on both sides of the piezoelectric vibrator in the laminating direction of the piezoelectric layers and electrodes varies largely depending on each individual piezoelectric vibrator in comparison with the thickness of the piezoelectric layers positioned between both sides in the laminating direction. Further, the thickness also varies largely between one end side and the other end side of the piezoelectric vibrator in the identical piezoelectric vibrator. The variation in the thickness causes a variation in the active displacement of the corresponding portions of the piezoelectric vibrator, which in turn unfavorably influences an ink discharge characteristic.
Accordingly, there is a piezoelectric vibrator without external electrodes formed on both side surfaces in the laminating direction. In this piezoelectric vibrator, since piezoelectric layers positioned on both sides in the laminating direction are not supplied with electric fields so that the corresponding portions are not actively displaced, the variation in thickness is unlikely to cause a variation in the displacement of the corresponding portions, which in turn reduces the influence upon the ink discharge characteristic. However, since the number of inactive portions which are not actively displaced, has increased, the displacement amount of the piezoelectric vibrator decreases as a whole.
The above problem occurs not only in an ink jet recording apparatus equipped with an ink jet recording head for discharging ink, but also in a liquid ejecting apparatus equipped with a different liquid ejecting head for ejecting a liquid other than ink.